This invention relates to a method of oil production and more particularly to a method for reducing the production of water from an oil-producing well.
Production of water along with crude oil is a problem that generally is tolerated so long as lifting and separating costs do not become uneconomical. In addition to increasing the expense of obtaining oil, the production of water also poses problems in its disposal. When water enters a borehole at a level different from that at which the oil enters, the water flow can be controlled by squeeze cementing or casing the producing formation and perforating through only to the oil production zone. In many cases though, the exact water entry point can not be determined or the water is commingled with the oil at the entry point to the borehole. A wide variety of methods for plugging off the water-producing portions of the formation, while not affecting the oilproducing formations, have been proposed and attempted with varying degrees of success.
One such method is described in U.S. Pat. No. 3,547,199 issued to H R. Froning, et al., on Dec. 15, 1970. This method generally involves the use of a foam to form a water block. The advantage of this method over other foam methods is that the foaming agent is oil-sensitive and therefore produces foam only in the water-bearing portions of the formation so that flow of oil is not obstructed. This selective characteristic of a water-blocking material has been the most difficult to obtain in practice.
Another material which is known to be useful for plugging subsurface formations is water-oil emulsion. An example of a plugging method intended to improve the injection profile of an injection well is found in U.S. Pat. No. 3,472,319 issued to McAuliffe on Oct. 14, 1969. In this patent, a mixture of oil, water, and an emulsifying agent is pumped into an injection well for the purpose of reducing flow of injected water through more permeable zones. Part of the selective nature of this disclosure is achieved by designing an emulsion which increases in viscosity with time.
Attempts have been made to use emulsions for the purpose of reducing the flow of water into oil-producing wells. One known method of causing the plugging effect to be selective is to inject only oil with an emulsifying agent in it into the formation. An emulsion then forms in-place in the formation wherever the oil with the emulsifier contacts water. While this in-place formation of emulsion in water-bearing zones has worked in some cases, it has not proved reliable enough to use on a regular basis. The ineffectiveness of this method is generally believed to be due to the difficulty of obtaining adequate mixing between the formation water and the injected oil-emulsifier mixture.